Small Molecule Walker Takes First Steps

A single molecule has been made to take its first steps, in a new development from Oxford University chemists.

'In the future we can imagine tiny machines that could fetch and carry cargo the size of individual molecules, which can be used as building blocks of more complicated molecular machines; imagine tiny tweezers operating inside cells,' said Dr Gokce Su Pulcu of Oxford University's Department of Chemistry. 'The ultimate goal is to use molecular walkers to form nanotransport networks,' she says.

As they report in this week's Nature Nanotechnology, Su and her colleagues at Oxford's Bayley Group took a new approach to detecting a walker's every step in real time. Their solution? To build a walker from an arsenic-containing molecule and detect its motion on a track built inside a nanopore.

'We can't 'see' the walker moving, but by mapping changes in the ionic current flowing through the pore as the molecule moves from foothold to foothold we are able to chart how it is stepping from one to the other and back again,' Su explains.
To ensure that the walker doesn't float away, they designed it to have 'feet' that stick to the track by making and breaking chemical bonds. Su says: 'It's a bit like stepping on a carpet with glue under your shoes: with each step the walker's foot sticks and then unsticks so that it can move to the next foothold.' This approach could make it possible to design a machine that can walk on a variety of surfaces.

Science fiction fans remember with some apprehension the first steps of the autofac from the 1955 Philip K. Dick short story of the same name:

The cylinder had split. At first he couldn't tell if it had been the impact or deliberate internal mechanisms at work. From the rent, an ooze of metal bits was sliding. Squatting down, O'Neill examined them.

The bits were in motion. Microscopic machinery, smaller than ants, smaller than pins, working energetically, purposefully - constructing something that looked like a tiny rectangle of steel.